The present invention relates to electrically operated valves and particularly to valves of the type operated by electromagnetic actuators such as solenoids. Solenoid operated electric valves are employed for a variety of applications and particularly in those fluid flow control applications where it is desired to maintain a proportional control of fluid flow in response to an electrical control signal. Typically, in such fluid flow control applications, a control circuit which may employ a microcomputer provides a control signal which has characteristics which vary dependant upon the desired changes in the flow of fluid through the valves.
In refrigeration systems it is commonplace to employ a thermal expansion valve for controlling flow of the compressed and liquified refrigerant from the condenser to provide refrigerant at a substantially reduced pressure to the evaporator inlet. Typically, thermal expansion valves have employed a liquid filled capsule sensing the temperature of the refrigerant discharging from the evaporator to control expansion of the fluid in the chamber to operate a pressure responsive moveable valve member for controlling the liquid refrigerant flow through the valve. Such diaphragm actuated thermal expansion valves are often used in automotive air conditioning systems for controlling refrigerant flow where rapid changes in operating conditions require a high degree of responsiveness by the valve. However, in automotive air conditioning systems, it has been desired to provide a valve which can do more than just react to changes in refrigerant temperature and to provide a valve which may be controlled in accordance with an electrical control algorithm or in response to electrical inputs via a microcomputer from sensors located in the compartment to be air conditioned. In particular it has been desired to provide an electric valve for an automotive air conditioning system which has the capability for proportional control responsive to a variable electrical control signal. It has been further been desired to provide such a valve which is low in manufacturing cost, easy to assemble and which is reliable in service over an extended period of time and capable of maintaining the seal integrity of the refrigerant system in service life.